SharePoint 2013 introduced a new feature called as Design Manager which helps customers customize SharePoint sites in a wizard-like approach.

Developers work with a designer or a design agency to brand SharePoint. First, the developer
receives the non-SharePoint branding assets (HTML, CSS, images etc) from the design agency. The design agency can create these files using any web design tool such as Dreamweaver or Microsoft Expression. The developer uploads the received files to SharePoint. Then, with a behind the scenes automatic process, SharePoint-specific assets (*.master & *.aspx) are generated. This process repeats until the branding task is complete. Then the developer exports the branding assets and creates a package (*.wsp) to deploy the custom brand to the production farm.